The present invention relates to a method for recycling scrap rubber comprising the steps of pyrolyzing scrap rubber to obtain a char material and milling the thus obtained char material. The present invention also relates to carbon black powders and carbon black pellets obtained by the method according to the invention. Moreover, the present invention relates to the use of said carbon black powder and to compositions comprising said carbon black powders.
Tyre recycling or rubber recycling is the process of recycling tyres (generally vehicles' tyres) that are no longer suitable for use on vehicles due to wear or irreparable damage (such as punctures). These tyres are also known as ‘End-of-Life’ (ELT) tyres. These tyres are among the largest and most problematic sources of waste, due to the large volume produced and their durability.
Used rubber tyres from sources such as automobiles and lorries include materials that, if successfully recycled, may be used for a wide variety of industrial uses. Extending the lifetime of the materials in such tyres is an area of intense interest, in particular, in the implementation of cradle-to-cradle products in the tyre industry.
Recycling tyres is, however, a difficult and costly process and as a result millions of tyres every year are worn out and accumulated, often in landfill sites. Scrap tyres are bulky and they take up a significant amount of space, even if compacted. Furthermore such used tyres also cause air pollution if burned.
One known way to recycle tyres is by means of pyrolysis. Pyrolysis uses heat in the absence of oxygen to decompose the tyre to yield steel, volatile gases and carbonaceous char. The carbonaceous char material is rich in carbon black which can be used for a number of applications.
However, an economically viable way to reprocess the scrap tyres into valuable end materials is not known. Examples of valuable products into which carbon black powder derived from scrap rubber could be compounded include car and light truck tyres, shoe soles and heels, conveyor belts, car- and houseware-mats, brake and clutch pads, V-belts, flooring, cable insulation, hoses.
Currently, the carbon black powder derived from scrap tyres has a number of problems associated with it, for example, a high volatile content precludes the prior art carbon black from being milled to a particle size of less than 40 micron This is because high amounts of volatiles reduces the ability of the char to be milled. In the art, a char material with a high volatile content is known as ‘brittle’. This so called brittleness is a key factor in determining the millability of a material, thereby making a char material progressively less millable as the volatile content increases. Thus such carbon black cannot be added to the said valuable products.
U.S. Pat. No. 5,037,628 discloses a pyrolysis method for reclaiming carbonaceous materials from scrap tyres by pyrolyzing the scrap tyres in a one step pyrolysis process to form a char material.
US2002119089 describes a one stage process for pyrolyzing scrap tyres involving the use of a rotating auger. The carbon black product has an average particle size of 0.125 mm making the product only suitable for low grade applications.
US 2008286192 describes a batch process for the two-stage pyrolysis of tyres. The char material is not milled but used directly in rubber formulations.
A problem with the char material obtained by pyrolyzing scrap rubber according to methods of the prior art is the inability to mill the char material to a particle size that is suitable for use in valuable products. Unacceptably high levels of volatiles that are present in the obtained char materials preclude the milling to carbon black powder.